The overall objectives of this project are to gain insight into the signal transduction mechanisms of the growth factor thrombopoietin (TPO) and its receptor, Mp1, as well as provide the applicant, Brian Lannutti with the scientific tools and career development necessary for a successful career in Basic science. During the next five years, Dr Lannutti will follow a research career development plan consisting of a program of educational sessions and a laboratory-based research project under the sponsorship of Dr. Jonathan Drachman and the consulting guidance of Drs. C. Anthony Blau, Gerry Krystal, and Paul Stein. The research plan is to define the molecular signaling mechanisms of Src kinases in response to Mp1 activation in order to better understand how these kinases are utilized during megakaryocyte development. Megakaryocytes arise in the bone marrow and produce platelets, the cells that mediate primary hemostasis. Precise regulation of platelet production is critical over the life of an organism and can be abnormal during disease states. The TPO/Mp1 signal pathway is essential for optimal growth of hematopoietic progenitors and is necessary for terminal differentiation of megakarocytes. The studies proposed here will assess the roles of Src tyrosine kinases with the goal of identifying those processes unique to megakaryocytopoiesis. The specific aims of this research project are to: 1) Identify which of the Src family members are activated in response to TPO and investigate their effect on megakaryocyte development; 2) Examine the role of Src kinases in Tpo-induced signaling by identifying molecules that interact with Lyn; and 3) Study how Src kinases regulate second messenger and downstream components important for cellular proliferation and differentiation that arise from Mp1 activation. Although an ambitious set of goals, the variety of techniques and methodology will help develop the breadth of Dr. Lannutti's scientific experience. Understanding the signaling mechanisms of Mp1 and its interactions with other signaling molecules may lead to novel approaches in the treatment of a number of hematologic and other diseases.